1. Field of the Invention
The present invention relates generally to a method and apparatus for simultaneous parallel readout and correlation of data on an optical disk and, more particularly, to a method and apparatus for addressing or illuminating multiple disk tracks and bits within each track containing data on the optical disk with a light beam encoded with external data, and for summing a light beam reflected from the disk, which reflected light beam represents the product of the external data and disk data.
2. Description of the Related Art
Optical disk memory is coming into very widespread usage. The advantages include large storage capacity, compatibility with existing memory access systems, and a remote or non-contact sensing head. Data is stored as digital bits (“1” or “0”), using mechanisms such as thermal ablation, phase change, and reversal of a domain in a magneto-optic medium. Applications include commercial audio and video, databases, and computer memory. Developments now allow such optical disks to be either read-only (information pre-stored), write-once and read many times (WORM type), and erasable/rewritable.
An important additional advantage of optical disk memory over a magnetic disk is the potential for optical readout of many channels of information in parallel. Present readouts are single channel and position the optical readout beam using mechanical-type mechanisms used in magnetic disk memory devices. The access time is slower and readout time is no faster than for corresponding magnetic media; these are commonly perceived disadvantages of optical disks.
Massively parallel optical readout could overcome these disadvantages. However, two obstacles present themselves. The first problem is that the rate of data readout would be increased by a factor equal to the number of parallel readout channels; this effective rate would presumably be a large multiple of the single-head readout rate (typically 25 Mbits/sec), which can cause data-rate overload (or mismatch) by the receiving device (e.g., the input to a computer or signal processing device) unless some measures are taken.
The second problem is that data encoding schemes and data formats for optical disks do not allow easy large-scale parallel readout using a single large-area optical beam. If multiple read heads are used, there is a practical limit on the order of ten channels, as well as a need to synchronize the multiple read heads. Therefore, there would be little advantage over a similar magnetic disk system. One scheme for overcoming this second problem is to store analog data on the optical disk using area modulation of a data cell with many binary bits to represent gray scale values. The disadvantage is loss of information capacity on a fixed-size optical disk. Moreover, this approach does not address the first problem of data-rate mismatch.